In a semiconductor device for power or the like, a semiconductor element such as an insulated gate bipolar transistor (IGBT), a metal-oxide-semiconductor field-effect transistor (MOSFET), an integrated circuit (IC) chip, or a large scale integrated circuit (LSI) chip is die-bonded to a lead frame for external terminal, and then electrically connected to a wire by a wire bond process or an inner lead such as a copper plate or a copper alloy by soldering, thereby allowing input and output of signals from and to the outside.
In a semiconductor device of a resin-molded type, a surface (mounting surface) of a lead frame on the side where a semiconductor element is mounted and a heat dissipation surface on the opposite side are sealed by an insulation resin using transfer molding. In particular, as for a semiconductor device for power, a semiconductor element that generates a large amount of heat is provided inside, and therefore an insulation resin for sealing is required to have high thermal conductivity. Accordingly, a semiconductor device is proposed in which, in a molding resin sealing process, the heat dissipation surface side is sealed by a high heat dissipation conductive resin having a thermal conductivity of 3 W/m·K to 10 W/m·K, and the mounting surface side is sealed by a low-stress resin or the like.
Here, molding with two types of resins, i.e., the resin for the mounting surface side and the resin for the heat dissipation surface side forms an interface between the two types of resins. An electric field is likely to concentrate on the interface, and the interface has poor adhesiveness, which causes peeling, leading to a problem that insulation property is deteriorated.
In order to solve the problem, there is technology disclosed in Patent Document 1 below. A semiconductor device of Patent Document 1 includes: a plate-like lead frame having first and second main surfaces and a pattern shape and having an external terminal therearound; a semiconductor element fixed on the first main surface; a heatsink provided so as to be opposed to the second main surface with a gap therebetween; and sealing resin for sealing the semiconductor element, the lead frame, and the heatsink. The sealing resin includes a primary sealing resin and a secondary sealing resin having higher thermal conductivity than the primary sealing resin. The secondary sealing resin has: a part that is in close contact with the second main surface and fills the gap between the lead frame and the heatsink; and a protrusion integrally connected to the above part and penetrating a gap of the lead frame accompanying the pattern shape, to protrude in a wall shape toward the first main surface side. The primary sealing resin is in close contact with the first main surface and encloses the semiconductor element, and also is in close contact with the protrusion.